1. Field of the Invention
The invention relates to a beacon for a star network, a sensor node in a star network and a method for operating a star network.
2. Description of the Related Art
Manufacturing automation imposes high requirements regarding latency between communications partners in wireless networks. This latency should be understood to be a period between the transmission of any message to one communications partner and the arrival of the message at the communications partner. Due to the special requirements in manufacturing, this latency should be kept as small as possible.
Architecture for a wireless network for use in manufacturing automation with a star network using a time slot method TDMA (time division multiple access) is known from the prior art, see Sahinoglu, Z. et al.: “TG4e drafting—Draft specification for IEEE 802.15.4e Factory Automation”, IEEE 802.15.4 document 15-09/401r3, July 2009. Hereinafter, the above document will be referred to as [1].
The star network comprises at least one central node (i.e., a gateway) and a plurality of network nodes connected to this in a star shape. Since manufacturing automation usually employs “intelligent” sensors, hereinafter, the network nodes are also referred to as “sensor nodes”. Here, intelligent sensors should be understood to be devices which, in addition to their sensory function also have functionalities that ensure integration in a network, bidirectional communication with other network devices and processing of the sensor data.
A wireless network is often the means of choice in manufacturing automation, because hardwiring the sensors would be too time-consuming and cost-intensive. Wiring also entails restricted freedom of movement and is a regular source of errors, which fact is not least attributable to the harsh environments encountered in industrial settings and which can give rise to further costs as a result of production outages. Here, wireless access to sensors and also to actuators avoids the aforementioned problems and also has the advantage of ensuring increased flexibility in the case of process changes or modifications to process devices.
The use of the teachings of document [1] in conjunction with the specifications in the IEEE Standard 802.15.4 ensures a reliable method for wireless and energy-saving transmission of sensor data.
A protocol using a superframe is defined for the communication of the sensor node and the gateway. A superframe defines an allocation of respective time slots to the individual sensor nodes. Here, at least one dedicated time slot for communication between the respective sensor node and the gateway is provided for each respective sensor node.
A periodic transmission of beacons by the gateway at the start of each superframe is provided for synchronization of an internal working clock pulse of the sensor node with the clock pulse rate of the superframe transmitted by the gateway superframe.
In order to optimize the high requirements on the brevity of the latency, the exchange of as much configuration information as possible is to a large extent avoided. This economy of data exchange is also supported by the provision of a production mode, also known as an “online mode”, which can be operated alternatively to non-productive modes, e.g., a configuration mode or a discovery mode. While an exchange of configuration information is provided in a configuration mode, in production mode, an exchange of this kind is kept as low as possible. Instead, when a production mode is running, the configuration information is extensively stored in the sensor node.
However, optimization in the above-described sense is achieved at the expense of the flexibility of the sensor network. For example, due to manufacturing requirements, it is not at present possible to notify newly added sensors in production mode to the gateway without leaving production mode and entering configuration mode, which involves the great disadvantage of the need to interrupt the manufacturing process during configuration mode.